Compressor system



April 1944- c. A. coRsoN 4 COMPRES SOR SYSTEM Filed March 27, 1943 1 2wINVENTOR E dfiuaJCSJI-Cordon.

Hi5 ATTORNEY.

Patented Apr. 4, 1944 comaassoa srs'ram Charles A. Corson, PaintedPost,-N. 1., anig nor to Ingersoll-Rand Company, NewYork, N. Y., acorporation or New Jersey Application March 27, 1943, Serial No. 480,783

8 Claims.

This invention relates to compressor systems and, more particularly, toa system of regulation for air or gas compressors.

It has been customary to operate air or gas compressors by driving themby electric or other motor controlled by an automatic pressure operatedswitch, so that when some predetermined maximum discharge pressure isreached the motor will automatically shut down to be restartedautomatically when the pressure drops to a predetermined minimum speed.This system has an advantage over other systems in which the compressor1s unloaded while the motor and compressor continue to idle, in that noelectric current is used during the stopped period. This advantagedisappears, however, if the stopping and starting occur very frequentlyfor the reason that during the starting period the motor draws excessivecurrent. It is thus seen that there is a point at which it would beadvantageous to merely unload the compressor without stopping it. Thislatter method of operation is known as "constant-speed operation, whilethe other is usually called the stop-start system. The stop-start"method is generally found desirable when the demand for air isrelatively low and the constant-speed" system i more advantageous duringperiods of greater demand and when the compressor loads and unloadsfrequently.

It is an object of this invention to provide a compressor system whichis adapted to operate on both the constant speed and the start-stopsystem, and in which the system to be used is automatically selected.

It is a further object of the invention to provide a system of thischaracter in which a minimum stopping period for the motor ispre-established so that the most economical of these types of operationmay result.

Other objects and advantages of the invention will become in partobvious and in part pointed out hereinafter.

In the drawing in which similar reference characters refer to similarparts and in which is shown a preferred embodiment of the invention,

Figure 1 is an end elevation of a compressor and its regulatingapparatus, certain portions of the regulator being shown in verticalsection and other parts being broken away to show more clearly theinternal construction and the operation of the various parts, theelectric wiring and piping being shown schematically;

Figure 2 is a top plan view taken along the line 2-4, looking in thedirection of the arrows in Figure 1 and showing portions of the switchand the controller: and

Figure 3 is a section taken along the line 3-4 of Figure 1 looking inthe direction of the arrows and showing the internal construction of theswitch mechanism of the controller.

Referring to the drawing, a compressor of a standard construction isshown at A having low pressure cylinders B and a high pressure cylinderC. In this instance, the compressor'A is shown driven by a suitableelectric motor D and the driving connection consists of a pulley E onthe electric motor D and a pulley F on the compressor A and a drivingbelt G.

The compressor A is provided withan intake manifold H leading to the lowpressure cylinders B. From these cylinders the air is. discharged intoan intercooler J through suitable piping K and thence by pipingconnection L to the high pressure cylinder C. High pressure air isconducted therefrom to a receiver M throuzh a discharge pipev N.

At the intake manifold H is provided a suitable unloading devicewhichconsists of a casing 0 flanged as at P for attachment to themanifold and provided internally with a balanced valve Q controllingcommunication between an outer chamber R connected with atmosphere, andan inner chamber S leading to the manifold H.

Valve Q is biased to its open position shown in the drawing by a springT. The valve is closed by pressure of a fluid actuated piston U bearingagainst a projection V on the valve. A suitable cylinder W is providedfor the piston U into which pressure fluid is adapted to be admittedfrom a chamber Y suitably connected, as will be described hereinafter,to the source of pressure fluid M.

A suitable source of current is provided from the electric mains i and 2having a main switch 3,1or connection with the motor leads 4 anad 5.Interposed between the switch 3 and lead 4 is a magnetic starting switchcomprising the armature 6 and the stationary contact I. As is customary,the armature 6 is biased to its open position by a spring 8. Tension ofthe spring I is overcome upon closing of the switch 3 by a solenoid 9included in a circuit bridged across the leads 4 and 5, preferablybetween the switch 3 and the contact 1 in respect of the lead 4, thebridged circuit include the conductors i0 and II leading to contacts I!and ll of a pressure switch l4 adapted to control stopping and startingof motor D. Cooperating with the contacts l2 and i3 there is provided acircuit closing member l5 operated by the switch. The pressure operatedswitch I4 is of conventional design and is operated by a plunger l6cooperating with a plate |1 against which a diaphragm I8 is adapted toexert pressure. The diaphragm i3 is housed within a casing l9 consistingof a flanged upper half 23 and a corresponding flanged lower half 2|,between which the diaphragm is clamped. Pressure fluid is admitted tothe space pressure switch I 4 is of the snap" variety and there is someset difierence between the pressures at which the plunger I6 is actuatedupwardly and downwardly. For instance the plunger l6 may be adapted tooperate at a receiver pressure .of 100 pounds and to be restored at apredetermined low pressure of 83 pounds. It is understood, of course,that the upward motion of the plunger l6 operates to open the circuit atswitch points I2 and I3 tending to-de-energize the solenoid 9 therebybreaking contact between the armature 6 and stationary contact 1.Normally, this will tend to stop the motor D by opening its circuit.Upon dropping of the plunger I6 at the predetermined low line pressure,the contact member I5 is adapted to restore the circuit at the switchcontacts l2 and I3 to re-energize the solenoid 9 and to close the motorcircuit.

The pressure switch I4 is also designed to operate a three way pilotvalve 24'which consists of a body portion 25 provided with upper andlower valve seats 26 and 21 respectively,

connected by bore 28. Within the bore 28 is disposed a valve stem 29provided at its ends with upper and lower valve heads 33 and 3|respectively. The stem 29 is o! sufllcient length so that only one oi.the valve heads 33 and 3| can be seated on the seatings 26 and 21respectively, at any one time. The stem 29 is arranged to be shifted sothat these valves seat on their respective seatings by means of a lever32 pivoted as at 33 on a bracket 34 formed integrally with the body 25.The lever 32 is adapted to press against an extension 35 of the stem 29so that as the lever 32 moves upwardly, valve 3| seats and the valve 33is unseated, and as the lever drops the valve 33 seats and the valve 3|is unseated.

The upper part of the body 25 is provided with a chamber 36 closed by aplug 31 and communicating through a passage 38 and a suitable pipe 39with the source of pressure fluid in the receiver M. The pipe 39 may, inthis instance. connect with the conduit 23 for this purpose.

The bore 28 in the pilot valve 24 is in communication with a tapped hole43 to which is attached a pipe or conduit 4| leading to the unloader atthe chamber Y. It will thus be seen that the pilot valve 24 is adaptedto alternatively connect the chamber Y and the unloader with the sourceof pressure fluid from the receiver M or with exhaust, depending uponthe seating of the valves 33 and 3|.

To operate the lever 32 the pressure switch I4 is provided with a pin 42extending to the exterior of the switch casing to engage the lever 32.The pin is actuated by the plunger i6 to move in the arcuate slot 43 sothat when the pressure switch |4 operates to open the circuit 01passageway 45 formed in the wall of the chamber Y, provided at one endwith a seat 46 cooperating with a ball check valve 41 disposed in acounterbore 48 and pressed to its seat by a light biasing spring 49.Counterbore 43 communicates with the chamber Y by hole 53. The valve 41is adapted to be unseated by fluid admitted from the conduit 4| underpressure, but is adapted to prevent escape of pressure fluid from thechamber Y. Exit from the chamber Y is provided by plug 5| having a verysmall oriflce 52 delaying emission of pressure fluid from the chamber.

Operation of the solenoid 9 is also controlled by a circuit bridgedacross the conductor II and the motor lead 4 and including theconductors 53 and 54respectively, and a switch 55 forming a part of asecond controller 56. Switch 55 is shown in section in Figure 3 andincludes a swinging contact I51 connecting with the conductor 53 and astationary contact I58 to which the conductor 54 is attached. Theswinging contact I51 is actuated by extremely small movement 01' aplunger I59 extending through the switch casing 63.

- The second controller 56 comprises a casing formed in two portions-anupper casing portion 51 and a lower casing portion 58, joining at twoflat faces adapted to receive between them a flexible diaphragm 59 ofany suitable material such as, for instance, rubber. Within the casingformed by the portions 51 and 58 are two chambers 63' and 6| divided bya partition 62 formed integrally with the upper half 51 and continued bythe lower partition 63 and the lower half 58. The chambers are dividedhorizontally by the diaphragm 59. The lower part of the chamber 6| isrelatively large as indicated at 64. The chamber 63 below the diaphragm59 is provided with anaperture 65 which communicates by conduit 66leading into the conduit 23 with the source of discharge pressure fluidin the receiver M. The diaphragm 59, therefore, is at all times withinthe lower part 01' chamber 63' exposed to the discharge pressure 01 thecompressor A.

The pressure against the diaphragm 59 is opposed in chamber 63' by aspring 61 bearing against a washer 68 overlying the diaphragm 59 andheld in place by a bolt 69. Tension on the spring 61 is adjustable bymeans of a screw 13 provided with a cap 1| fitting the upper end of thespring 61. The screw 13 is threaded in the upper wall of the uppercasing half 51 at, the threaded aperture 12. Adjustment of the screw ismaintained by a lock nut 13.

Chamber 64 is adapted to receive pressure fluid through an orifice 14 inthe wall of the chamber and connected by a pipe 15 and a conduit 16 tothe conduit 4|. Chamber 64 thus receives pressure fluid under thecontrol of the pilot valve 24 and the controller l4. Likewise under thecontrol of the pilot valve 24 pressure fluid is exvalve 19 controlling apassageway 99 leading toa chamber 9I. A reducing pipe plug 92 in chamber9| is provided with a nipple 99 leading to the conduit I5. Pressure ondiaphragm 59 within the chamber 54 is opposed by a coil spring 94bearing against washer 95 bolted to the diaphragm 59 by means of thelarge headed bolt 99.

The compression of spring 94 is regulated by means of the threaded screw91 passing through the threaded aperture 99 in the top wall of thecasing half 51. In this instance the adjustment is set by means of shims99 under the head of the screw 99.

At such times as the pressure under the diaphragm 59 is unable towithstand the pressure of the springs 51 and 94, the bolts 99 and 95rest upon stops 99 and 9|, respectively, which are formed integrallywith the lower casing half 59.

Motion of the diaphragm 59, due to the pressures thereunder, is adaptedto be transmitted to the switch 55. For this purpose the screws I9 and91 are hollow and provided with push rods 92 and 99, respectively,bearing against the stems of the bolts 59 and 95, respectively. At itsupper end push rod 92 is provided with a nut 94 cooperating with a Ushaped lever member 95 at an aperture 95. Likewise, push rod 99 isprovided with a nut 91 cooperating with the lever 95 at an aperture'99.

Push rod 92 bears against the top of the stem of bolt 59 and is held incontact therewith by a light leaf spring 99. Likewise, the push rod 93is held in contact with the corresponding bolt 85 by means of a lightspring I99.

The U shaped lever 95 is Journaled at the ends of its arms on a bearingrod I9I mounted in a bracket I92 at the top of the upper casing half 51upon which bracket also are mounted the leaif springs 99 and I99. Motionof the U shaped lever 95 is adapted to transmit motion of the diaphragm59 to the plunger I59 on the switch 55. To this end the lever isprovided with a recess I93 to receive the plunger.

The weight of the lever 95 is counterbalanced by a light coil spring I94seated on the top of the switch 55 and contained in a pocket I95 of theU shaped lever 95.

As can be readily understood from the above description, the actuatingforce for the switch 55 is the pressure of the springs 99 bearingdownwardly. When this pressure is overcome by upward motion of the pushrods 92 and 93, the switch is released by the spring I94. The switch 55is extremely sensitive and the contacts I51 and I59 are closed by anextremely slight motion of the plunger I59 of the order of one or twothousandths of an inch.

Under certain conditions, as will be described hereinafter, it isdesirable that the switch or controller I4 be operated at a close rangeof pressures in the receiver M instead of at the wider range as abovereferred to. To this end, a range changing device I95 is provided, whosepurpose is to change the operational pressure range of the plunger I5.This is accomplished by reducing the effect of the high pressure on thediaphragm I9. The range changing device I95 consists of a cylinder I91provided with an upper head I99 and a lower head I99 and a piston II9'fitting the bore of the cylinder. The upper head I99 is provided with apassage II9 communicating by means of a pipe III with the manifold H.The lower head I99 is provided with a valve seat 2 in bore III, whichcommunicates with the space in the casing I9 under the diaphragm I9 bymeans of a pipe 4. A restrictive orifice III is provided in the bore IIIfor the purpose of controlling the flow of pressure fluid throughthepipe H4. The bore of the cylinder III is provided with a vent I I9 toatmosphere by means of which pressure fluid entering the bore may escapeto the open air when the valve seat H2 is opened at a valve III formedintegrally with the piston I I9. Normally, the piston I I9 is biased bymeans of a spring I I9 to its closed position. I

The apparatus above described has been adapted to permit the compressorA to operate at constant-speed" during the periods of normal demand,that is to say, without shutting down. Additionally, it enables thecompressor to convert automatically to operation at start-stop" duringperiods of low demand such as would be found perhaps at night.

Under all circumstances it will be noted that when the .pressure in thereceiver M rises to some predetermined value, as for instance 100pounds,

the diaphragm is forced upwardly to cause the controller I4 to open thecircuit including contacts I2 and I9. Simultaneously, the pilot valve 24is operated to open communication between the supply conduit 29 andconduit 4I thereby admitting motive fluid through the passageway 45 pastthe check valve 41 and through aperture 59 into the chamber Y, whereuponthe piston U is forced against the pressure of the spring T to move theintake valve Q to closed position. Admission to the inlet manifold H isthereby cut of! from atmosphere and the compressor A is therebyunloaded. The motor D, however, does not immediately stop because itscircuit is not opened by operation of the controller I4. The switchpoints 5 and I are held closed by the solenoid 9 since its circuit isstill closed at the switch 55.

As has been indicated above, operation of the pilot valve 24 by thecontroller I4 also controls the second controller 55 in the followingmanner: Motive fluid from the receiver M is constantly in communicationwith the chamber 59' under the diaphragm 59, which at a predeterminedhigh pressure would tend to overcome pressure of spring 51 and to liftthe push rod 92 upwardly to release the U shaped lever. This lever is,however, normally prevented from moving upward by pressure of holdingthe lever down through the medium of the push rod 99 and the nut 91.Therefore, if the U shaped lever 95 is to release the switch 55 at all,pressure holding the push rod 92 in raised position must be maintaineduntil the push rod 93 is raised. The mechanism operating the push rod 93is, therefore, a timing mechanism which, in conjunction with theoperation of the push rod 92, determines whether the switch 55 is toopen or not. To this end, the chamber 54 is adapted to be filled slowlyat some predetermined rate. with pressure fluid from the receiver M.This is accomplished through the medium of the pilot valve 24 which,while admitting motive fluid to operate the unloader, also admitsthrough the conduit I5 and pipe 15 motive fluid to the chamber 54. Thesize of the orifice I4 through which the motive fluid passes is suitablyselected so that in some given time the chamber '54 will build uppressure to a suitable value to raise the diaphragm 59 thereby liftingthe push rod 99 to release the U shaped lever 95.

Assume that the operating range of th controller I4 is setat 20 pounds,that is to say, to operate the pilot valve 24 at 100 pounds per squareinch and to restore it at 80 poundsreceiver pressure, the secondunloader may be set so that the push rodjl, .upon a drop in pressurefrom 100 pounds to 98 pounds, will re-engage the lever 95 so as toprevent-its operation. Simultaneously, by suitable selection of the sizeof the nozzle 14 and tensioning of the spring 84, the pressure may beregulated to build up within 30 seconds in the chamber 64 so as to startraising the push rod 93. Thus it will be seen that if the switch 55 isto be open under these conditions. the receiver pressure will have todrop somewhat less than 2 pounds in 30 seconds, in which case both pushrods 92 and 93 will. be in raised position simultaneously to releaselever 95,-. In that case the circuit of the holding c911 [will be openboth at the switch 55 and at the contacts I2 and I3 which causes theswitch to open at contacts 8 and I to stop motor D.

Conditions just described may be considered those of low demand and theydetermine, by means of the controller 56, a minimum stopping period forthe motor D. Under these specific conditions, that is, with the pressuredropping at the rate of something less than 2. pounds in 30 seconds, itwill be seen that the minimum stopped period for the, motor D will be 5minutes for a pressure range of 20 pounds, the assumed settlng oi thecontroller l4.

It will be noted that while the relativ motions of the push rods 82 and93 may client the operation of the switch 55 to open the circuit of theholding coil 9, they cannot under any condition operate to close thecircuit of that coil, in-. asmuch as the circuit including the switch'55,

also includes the switch contacts 6 and 1. There-.

fore, the switch 55 can never start up the motor D once it has stopped.In other words, when the controller 56 has operated to shut down themotor D, restarting of the motor can only-"be effected by the controllerH which, as one of its down before the pressure in the chamber '64 hashad time to build up to release the lever. The switch 55, therefore,stays closed. It may be said, therefore, that the controller 56 isoperated by the'rate of drop in pressure per unit of time to openandclose the circuit of motor D.

. Under such conditionathe controller H has the-effect of operating onlythe intake unloader, which is effected entirely through the pilot valve24. Thus, during periods of great demand, the motor Doperates-continuously while the intake unloaderperformsthe function ofloading and unloading the compressor A. i It will be seen that the motorD is stopped by operation of controller 56 at some definite period afteroperation of the controller 14. Correspondingly, the compressor is alsofirst unloaded by the intake unloader. It is considered desirable, as itwell known in the art, that the unloader should keep the compressorunloaded while the motor D is starting, since it is uneconomical tostart any motor under load. Accordingly, upon operation of thecontroller l4 to restart the motor D, the pilot valve 24 operates torelease the motive fluid from the chamber Y. Under these conditions, thecheck valve 4! is held closed by the spring .49 and the exhaust ofmotive fluid is permitted only through the small orifice 52 of a sizewhich would allow the lapse of several seconds before the pressure inthe chamber Y will drop sufficiently to permit the compression of thespring T to' throw the valve Q to its open position.

While the chamber 64 is arranged to be. filled with pressure fluid veryslowly by way of the orifice 14, it is preferablyexhausted rapidly byway of the check valve 19 when the pilot valve 24 is restored to itsnormal position exhausting the air-in the line .4l.

During the periods of great demand for pressure fluid it is oftenconvenient to operate the compressor A at a closer pressure range thanwhen running start-stop and this is the purpose of the range-changingdevice I06. While the compressor A is running unloaded, the pressure inthe manifold H is subatmospherlc. This suction is transmitted to thebore of the cylinder I01, lifting the piston III! to uncover the valveseat H2 and permitting air to escape through the pipe H4 slowly throughthe orifice H5 to atmosphere by way of the port 6. The escape of air inthis manner has the effect of reducing, to a certain extent, thepressure under diaphragm l8 since admission to the space under thediaphragm is also restricted by the orifice 22. Thus, while the plungeri6 may have been forced upwardly by a pressure of 100 pounds per squareinch to actuate the controller l4, subsequent action of the intakeunloader and the rangechanger I08 may immediately drop the pressureunder the diaphragm ii to a value, for instance of 90 pounds. Then,-upon reduction of the pressure in the receiver M to 90 pounds, therewill be a corresponding reduction in the pressure under the diaphragmto, let us say, 80 pounds, which will cause the controller I4 tooperate, thereby reloading the compressor A. In this manner, the

pressure operating range may be changed from, for instance 20 pounds to10 pounds.

As will be obvious, the range-changing device I06 is not in effect whenthe motor D is operating on the stop-start" conditions for, in suchcases, the intake manifold H does not remain under vacuum for any greatlength of time while the motor D is stopped.

The change of range above referred to is desirable inasmuch as duringlarge demand periods it is desirable to keep the pressure in thereceiver M fairly constant, while under stop-start conditions constantpressure is not so desirable as it causes more frequent starting andstopping of the motor D.

I claim:

1. A compressor system including a compressor. a driving motor therefor,acontroller operated by the compressor discharge pressure adapted tostop the motor at a predetermined high pressure and to restart the motorat a predetermined low pressure, a compressor unloader operated bypressure fluid controlled by said controller to unload thecompressor atsaid predetermined high pressure and to reload the compressor at thepredetermined low pressure, and a second controller to delay .the stoppng of the motor after operation of the first controller and topre-establish the minimum stopping period of the motor.

2. A compressor system including a compressor, a driving motor therefor,a controller operated by the compressor discharge pressure adapted tostop the motor at a predetermined high pressure and to restart the motorat a predetermined low pressure, a compressor unloader operated bypressure fluid controlled by said controller to unload the compressor atsaid predetermined high pressure and to reload the compressor at saidpredetermined low pressure, means to delay operation of said unloader toreload the compressor for a givenperiod after said predetermined lowpressure is reached, and a second controller adapted to delay stopp orsaid motor at said predetermined high pressure, said controllerincluding means for pre-establishing the minimum stopping period of saidmotor controlled by the rate of drop in the compressor dischargepressure when the compressor is unloaded by said unloader.

3. A compressor system, including a compressor, a device for unloadingthe compressor, a motor for driving the compressor, a pressure fluidoperated controller for stopping and restarting the compressor motor andhaving a predetermined pressure range, a second pressure fluid operatedcontroller for the motor having a shorter pressure range than the firstsaid controller and provided with a timing mechanism controlled by theflrst controller to pre-establish the minimum stopping period 01' themotor.

4. A compressor system, including a compressor, an electric drivingmotor therefor, a magnetic switch mechanism for controlling said motor,a controller operated by the compressor discharge pressure for saidswitch mechanism for stopping and restarting the motor, and meansassociated with said switching means for preestablishing the minimumstopping period of the motor, said means being controlled by the rate ofdrop in the compressor discharge pressure.

5. A compressor system, including a compressor, an electric drivingmotor therefor, a magnetic switch mechanism for controlling said motor,a controller operated by the compressor discharge pressure for saidswitch mechanism for stopping and restarting the motor, a compressorunloader operated by the controller, and means associated with theswitch mechanism for pre-establishing'the minimum stopping period of themotor, said means being controlled by the rate of drop in the compressordischarge pressure when the compressor is unloaded.

8. A compressor system, including a compressor, an electric drivingmotor therefor, a controller for said switch mechanism operated by thecompressor discharge pressure to stop the motor at a predetermined highpressure and to restart the motor at a predetermined low pressure, acompressor unloader operated by pressure fluid and controlled by saidcontroller to unload the compressor at said predetermined high pressureand to reload the compressor at the predetermined low pressure and asecond controller associated with said switch mechanism to delaystopping of the motor after operation of the first said controller andto pre-establish the minimum stopping period of the motor.

'7. A compressor system including a com pressor, an electric drivingmotor therefor, a switch mechanism for controlling the operation of saiddriving motor, a controller for said switch mechanism operated by thecompressor discharge pressure to stop the motor at a'predetermlned highpressure and to restart the motor at a predetermined low pressure,'acompressor unloader operated by pressure fluid controlled by saidcontroller to unload the compressor at said predetermined high pressureand to reload the compressor at said' predetermined low pressure, meansto delay reloading operation of said unloader for a given period aftersaid predetermined low pressure is reached, and a second controllerassociated with said switch mechanism adapted to delay stopping of saidmotor at said predetermined high pressure, said controller includingmeans for pre-establishing the minimum stopping period of said motor andcontrolled by the rate of drop in the compressor discharge pressure whenthe compressor is unloaded by said unloader.

8. A compressor system, including a compressor, an electric drivingmotor therefor, a switch to control the circuit of said motor, a holdingcoil for said switch, a controller for said holding coil operated by thecompressor discharge pressure to stop the motor at a predetermined highpressure and'to restart the motor at a predetermined low pressure, acompressor unloader operated by pressure fluid controlled by saidcontroller to unload the compressor at said predetermined high pressureand to reload the compressor at said predetermined low pressure, and asecond controller associated with said holding coil adapted to delaystopping of said motor at said predetermined high pressure, said secondcontroller including means for pre-establishing the minimum stoppingperiod of said motor and controlled by the rate of drop in thecompressor discharge pressure.

CHARLES A. CORSON.

